White-plumed Antbirds (Pithys albifrons) are small, obligatory ant followers found in the Amazon Basin and Guiana Shield. They rely on their small size to forage near the front of ant swarms (Eciton spp.) where they prey on escaping insects and try to avoid physical confrontations with larger and more dominant ant-following bird species. They are unique in that they have the longest known molt duration among passerines (approximately 310 days; Johnson and Wolfe 2014). Pithys albifrons undergo a complete preformative molt, making the separation of formative (FCF) and definitive basic (DCB) plumages nearly impossible. Separating age classes after FCF is made easier during active wing molt where definitive prebasic (DPB) and second prebasic (SPB) individuals can often be separated (see below for details).

Pithys albifrons

FCJ - First Cycle Juvenile

First cycle juvenile (FCJ) individuals have loosely textured plumage with orange tips throughout the coverts. Most strikingly, FCJ individuals lack the white head plume found on older birds. FCJ birds will quickly initiate the preformative molt (FPF) which takes substantial time to complete.

FPF - First PreFormative

Juvenal plumage is slowly replaced with more densely textured and gray feathers during the preformative molt (FPF). It is easier to separate FPF from definitive prebasic (DPB) individuals during the beginning stages of molt. This is due to the abundant and easily identifiable juvenal plumage during earlier stages of FPF, thereby providing much more obvious contrast with gray and more dense formative plumage. During the latter stages of theFPF, it becomes nearly impossible to separate FPF from DPB individuals; in such circumstances, practitioners can use unknown molting codes (UPU) or simply an after juvenile code (FAJ).

FAJ - After First Cycle Juvenile

Fomative (FCF) and defintive basic (DCB) plumages are indistinguishable due to the complete nature of the preformative molt (FPF). Because we can't distinguish FCF and DCB individuals, we can use the "a" code, for "after a given plumage". In this case, we would classify the age as after the juvenile plumage (FAJ).

DPB - Definitive PreBasic

Species with complete preformative molts, such as Pithys albifrons, are difficult to age when they are not molting (i.e. we can't separate FCF from DCB individuals). When these species molt, it provides opportunity to use more precise age codes. In this last example, we can clearly see that the older plumage is not juvenal (see FCJ and FPF examples above), thus, it must either be formative or definitive basic. Given that the older plumage is being replaced (P1 and P2) by fresh and strikingly gray feathers, this individual is at least beginning the second prebasic molt. Because we can't differentiate second from subsequent prebasic molts, we use the more general DPB code (definitive prebasic molt).

© 2019 by Jared D. Wolfe

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